During internal combustion piston engine operation, the piston moves between a bottom dead center (BDC) and a top dead center (TDC) position. When operating near the TDC position, depending on various parameters, there may be physical interference between the engine's valves and the piston.
U.S. Pat. No. 6,401,675 describes calculating control ranges for variable valve timing and variable valve lift actuators in the event one of the actuators degrades to prevent such interference from occurring.
The inventors herein have recognized a disadvantage with such an approach. In particular, the system actuators may be functioning, yet various sensors may be degraded. As such, if a signal provides incorrect information, the controller may calculate that no interference is present when in fact such interference may occur. Alternatively, the controller may calculate that interference is likely and adjust control signal to inefficient position, when in fact no such interference is likely. This can lead to engine degradation in one case, or inefficient operation in the other.
One approach to overcome the above disadvantage uses a method for controlling valve operation of valves coupled to a cylinder of an internal combustion engine with a piston, the method comprising:
using at least a sensor coupled to the engine to indicate potential interference between the piston and the valve when the valves are operating in a condition where such interference is possible;
determining whether the sensor has degraded; and
in response to a determination that said sensor has degraded, adjusting operation of the valves to a condition where there is no potential for interference.
The inventors herein have recognized other disadvantages with prior approaches. Specifically, it may be important to consider other actuators in detecting interference, and in taking action to reduce potential interference during operation, especially in the case of sensor or actuator degradation.
For example, in one approach, the above disadvantage is overcome by a method for controlling valve operation of valves coupled to a cylinder of an internal combustion engine with a piston, the engine having a device to adjust compression ratio of the cylinder, the method comprising:
indicating potential interference between the piston and the valve based on engine operating conditions; and
in response to said indication, reducing compression ratio of the cylinder by adjusting said device.
In this way, by using compression ratio, it is possible to reduce potential interference. Furthermore, in the case where the valve lift/cam actuator may have degraded, by using the compression ratio, it is still possible to provide engine operation, rather than shut down engine operation.
The inventors herein have also recognized other disadvantages with prior approaches. Specifically, the approach described in '675 starts acting only after a mechanism failure has been declared, which usually occurs on a timescale much longer an engine event, or two. Moreover, because one actuator is assumed non-operational, there is no possibility for the '675 system use coordination of the two actuators to reduce the possibility of interference. Also, a failed actuator condition would also prevent the '675 system from reacting if the fault is in the scheduling subsystem. Finally, with aggressive scheduling, the trajectory can lead through a clearance violation zone even if both actuators are operating within normal design limits. This means that either very tight design specifications will have to be imposed on the actuators or the valve-to-position clearance safety margin will have to be very wide, possibly preventing optimal scheduling.
Various of the above disadvantages are overcome by a computer storage medium having instructions encoded therein for controlling valve operation of valves coupled to a cylinder of an internal combustion engine with a piston, the engine in a powertrain in a vehicle on the road, said medium comprising:
code for indicating potential interference between the piston and the valve; and
code for adjusting both of said valve timing and valve lift to reduce said potential for interference in response to said indication.
An advantage of the above aspect is that it is possible to react quickly to the possibility of hardware damage, while reducing any delayed reaction.
Another advantage of the above aspect is that it is possible to allow optimal valve settings, even if the actuators have differing actuation rates, and even if the actuator controllers have transient responses that might cause intermittent valve clearance violations. Further, it is possible to utilize both available actuators to reduce potential clearance, if desired.